This is right actually. The vast majority of Turin's population support Torino, this is attributed to the history of the town and the loyalty of the fans themselves.
If we return back to the 30's and 40's of the previous century, we'll find that Torino was amongst the greats in Italy. Also, it is no secret that "Grande Torino" widely considered the best ever team in Italian football history, won five other straight scudetti between 1942/43 and 1948/49. Hence, it wasn't a surprise that most of the football fans in Turin supported Torino.
But, in 1949, the disaster happened. All the team members were killed when their plane crashed, and ironically, just one player was lucky enough to keep his life because he was out for an injury. The club never recovered and they have been suffering until now.
The amazing part of the saga is that Torino are still very popular despite their situation, and also more popular than the greatest Italian team ever; Juventus, who is located in the same town; Turin.
Indeed, this isn't an exclusive speciality of Turin, but lots of European towns like Liverpool, Manchester, Barcelona, etc...are nearly the same as Turin.